1. Field of Invention
This invention relates to the field of setting, calibrating, and verifying an occupant classification system (OCS) threshold. More specifically, this invention relates to a simplified and accurate method of setting an OCS threshold for a type of vehicle seat and then calibrating and verifying seats of the same type following manufacture.
2. Background
To limit the risk of death or serious injury in the event of a crash, many vehicles include passenger airbags, which are designed to deploy under certain crash conditions. Various types of sensors and crash criteria are commonly used to detect crash conditions for which passenger airbag deployment is desirable.
It is known that, even given a crash condition for which passenger airbag deployment is desirable, deployment of an airbag can itself cause injuries when the occupant of the passenger seat is a small child or infant. Accordingly, federal regulations have been developed requiring a system for determining whether a passenger seat is occupied by a small child or an infant, in which case airbag deployment should be suppressed.
In addition, if the passenger seat is unoccupied, deployment of the passenger airbag is unnecessary. Unnecessary deployment of the passenger airbag can increase the cost of repairing the vehicle.
Vehicle occupant detection systems judge whether, and how forcefully, to deploy a restraint such as a passenger airbag. One fundamental parameter in judging deployment is the weight of the seat occupant, as weight may be used to distinguish between an adult and an infant or small child. For example, Federal Motor Vehicle Safety Standard (FMVSS) 208 requires that an airbag be suppressed for a child less than six years old, but be deployed for an adult in the 5th percentile. A 5th percentile adult weighs, for example, 103-113 pounds standing, with a seated weight of about 77-85 pounds. A 6-year-old child weighs, for example, 52.5 pounds when seated. Thus, a separation exists between the seated weight of a small adult and a six year old child.
A known way of estimating occupant weight is by measuring pressure in a fluid-filled bladder disposed in or under a foam seat cushion. Increased weight on the seat increases pressure in the bladder. A pressure sensor connected to the bladder generates output signals indicative of pressure in the bladder and therefore occupant weight. Because a separation exists between the seated weight of a small adult and a 6-year-old, a separation similarly exists for pressure in the bladder and therefore the output signals of the pressure sensor.
In a crash situation, a microprocessor determines whether the output signals from the passenger seat pressure sensor exceeds a threshold value indicative of adult occupancy. If so, deployment of the passenger airbag is enabled. If not, it is assumed that the passenger seat is empty or the occupant of the seat is a small child or an infant, and deployment of the airbag is suppressed or limited accordingly.
Vehicle manufacturers must calibrate and verify calibration of these occupant detection systems. A conventional calibration and verification system applies a weight to the vehicle seat. Data corresponding to the applied weight is output from the seat's pressure sensor. The data is processed by a controller of the occupant detection system and calibration values are calculated, which include the threshold value indicative of adult occupancy. The calibration values are typically stored in an EEPROM. The weight is applied to the seat again, and the verification values are calculated again. If the calibration and verification values for the weight applications are within a specified tolerance, the occupant detection system is acceptable for use. This calibration and verification system can also be used to program the controller of the occupant detection system.